The present invention relates generally to complementary metal oxide semiconductor (CMOS) integrated circuits for low current, signal level translation applications. More particularly, the present invention is directed to translator circuit arrangements that are useful for providing a square wave output signal with preserved duty cycle, whether the input signal is a square wave or a sinusoid. These circuits are especially useful when translating a sinusoidal signal generated in a low current inverting stage.
Signal level translation is generally defined as a shifting of a given signal having a set peak-to-peak signal amplitude to another, different peak-to-peak signal amplitude. For most digital applications, a square wave output signal is desired, even though the input signal may exist either as a square wave or as a sinewave. The square wave output signal is desireable for noise immunity and for interfacing with other digital circuitry that is commonly found in present-day radio and computer circuitry.
Various attempts have been made to provide suitable translators, but these translators have proved to be seriously deficient in one or more of the following operational characteristics, including high current consumption, poor preservation of duty cycle, and poor noise immunity.
One known type of translator relies upon an inverting stage, consisting of a complementary pair of devices, that is coupled to an input signal through a DC blocking capacitor. This inverting stage is supplied by a voltage source and includes a resistor coupled between output and input. Such a translator arrangement operates the two devices as a Class A stage and suffers from very high current consumption. Typically, the input voltage is several volts smaller than the supply voltage and consequently both devices will always be on and dissipate a large current.
Accordingly, there exists a need for a low current translator suitable for use with a high frequency (10-20 MHz) sinusoidal or square wave input signal that provides an output signal that maintains a precise duty cycle with low noise.